1. Field of the Invention
The present invention relates to an organic electroluminescence (EL) display apparatus, a method of producing the same, a method of repairing a defect, and a repair apparatus. In particular, the present invention relates to a method of selectively repairing a pixel having a defective portion in which a cathode electrode and an anode electrode of an organic EL device are short-circuited, so as to enhance a yield of a repair display.
2. Description of the Related Art
In recent years, an EL display apparatus (organic EL display) has been developed actively, which is capable of being made thinner than a cathode ray tube (CRT), obtaining a wider viewing angle than a liquid crystal display apparatus, and being reduced in weight and cost.
The organic EL display generally has a configuration in which an organic light emitting layer is interposed between an anode electrode and a cathode electrode, and light is emitted when a current flows between the electrodes by an external drive circuit. Hereinafter, a device including a pair of electrodes and an organic light emitting layer will be referred to as “organic EL light emitting device” or “organic EL device”.
In a simple matrix system, an anode electrode and a cathode electrode interposing an organic light emitting layer are arranged so as to constitute an XY matrix electrode, and are orthogonal to each other. A crossing point of the XY matrix electrode constitutes one pixel.
According to operations of an active matrix organic EL display with a thin film transistor (TFT), a scanning pulse voltage is applied successively to a scanning line in an X-direction, and TFTs whose gate terminals are connected to the scanning line are turned on at a time. Simultaneously, a signal voltage is applied to a signal line in a Y-direction, and charge is accumulated in a capacitance of each pixel through the TFT. When scanning of one line is completed, the TFTs are turned off, and the charge accumulated in a pixel capacitance remains as it is. As a result, an arbitrary applied voltage is set.
In the organic EL display, in a case where the anode electrode and the cathode electrode interposing the organic light emitting layer are short-circuited, an organic EL device in that portion does not emit light, with the result that a non-lighting defect occurs.
The short-circuit between the electrodes is caused by adhesion of foreign matters, a pin-hole of an organic light emitting layer, or the like. Generally, the thickness of the organic light emitting layer formed between the electrodes is very small, that is, about several 10 nm to 100 nm, and a large number of non-lighting pixels are likely to be caused by the short-circuit between the electrodes. In the organic EL display, it is very difficult to prevent foreign matters of a sub-micron or less from adhering to an inside of a surface of a display, so there is a demand for the countermeasure against a non-lighting pixel.
On the other hand, it is known that such a non-lighting defect can be lit normally by burning out a short-circuited portion with a laser so as to insulate the short-circuited portion. However, it is difficult to find in which place of a pixel a short-circuited portion is present.
Japanese Patent Application Laid-Open No. 2004-199970 discloses a method of specifying the position of a heat generation portion caused by a short-circuit in a high-magnification field of view of an infrared temperature image detection microscope. However, according to the method, a step of laser repair (burning repair) is complicated and takes a long time, which increases the cost of one panel to a large extent.
As another method of burning repair, a method of repairing a short-circuited portion during aging is known. According to this method, in a manufacturing process of an organic EL device, aging processing of applying a voltage between an anode electrode and a cathode electrode is performed to open and break a film defective portion previously. The opening and breaking refers to making a defective portion non-conductive. The opening and breaking is considered to be caused by a phenomenon in which an electrode corresponding to a film defective portion is broken and opened (insulated) by Joule heat generated during aging or oxidized to be made non-conductive. The film defective portion subjected to the opening and breaking becomes a local non-light emitting state. However, the film defective portion is smaller than the whole pixels, so the film defective portion does not influence the quality of a display.
Japanese Patent Application Laid-Open No. 61-114493 discloses an aging method for an inorganic EL device as the method of performing opening and breaking by the aging. According to this method, a DC voltage is applied as a first aging step, whereby a defective portion present in a panel is broken in a small region.
Further, Japanese Patent No. 2,818,255 proposes the following method. That is, aging is performed such that an organic EL device is successively supplied with a DC forward voltage and a DC backward voltage, which are within a range of 1×104 to 1×107 (V/cm), for one second or longer, respectively, as a first aging step. After that, as a second aging step, a DC forward voltage is applied for a longer period of time than the first aging step.
Further, Japanese Patent No. 3,562,522 discloses a method in which a breakdown voltage of a defective portion and a breakdown voltage of an organic EL device are obtained, and then, an aging step is performed with a voltage range between the breakdown voltages being set to be a range of an applied voltage in the aging processing.
According to any of the above-mentioned methods, a voltage is applied to a normal pixel. Therefore, device degradation of a normal pixel is caused, which leads to inconvenience such as decrease in panel luminance and occurrence of display unevenness Further, in a case where a panel area is large, a current flowing through a panel increases. Therefore, power source wiring itself generates heat to be disconnected, and device degradation may be caused by the heat generation of a panel. Actually, it is difficult to apply the aging processing.